Tyre for vehicle wheels

ABSTRACT

A tyre for vehicle wheels, in particular for heavy load vehicle wheels, has a tread band including an annular central portion astride an equatorial plane and two annular shoulder portions arranged on axially opposite sides with respect to the annular central portion. The annular central portion is separated from a respective annular shoulder portion by a respective circumferential groove. The annular central portion includes a plurality of blocks arranged along at least one circumferential row between two circumferential grooves and at least one transversal sipe arranged between two circumferentially consecutive blocks. The transversal sipe has a main surface oriented in a substantially radial direction and provided with at least one deformation defining, in the adjacent blocks, respective portions of mutual constraint. The deformation has an overall decreasing width from an axial end of the sipe to a central zone thereof and has a radial extension smaller than that of the aforementioned main surface.

The present invention relates to a tyre for vehicle wheels, inparticular for heavy load vehicle wheels.

The invention also relates to a tread band for one such a tyre, inparticular a premoulded tread band for covering worn tyres.

A tyre for vehicle wheels intended to be used on heavy load vehiclesgenerally comprises at least one carcass structure comprising astructure ply formed by reinforcing cords embedded in an elastomericmatrix. The carcass ply has end edges respectively engaged with annularanchoring structures. The latter are arranged in the zones of the tyreusually identified with the name of “beads” and normally consist each ofan annular substantially circumferential insert on which at least onefilling insert is applied, in radially outer position thereof. Suchannular anchoring structures are commonly identified as “bead cores” andhave the task of keeping the tyre well fixed to the anchoring seatspecifically provided in the wheel rim, thus preventing, in operation,the radially inner end edge of the tyre coming out from such seat.

At the beads specific reinforcing structures may be provided having thefunction of improving the torque transmission to the tyre.

In a radially outer position with respect to the carcass ply, a beltstructure comprising one or more belt layers is associated, said beltlayers being arranged radially one of top of the other and havingtextile or metal reinforcing cords with crossed orientation and/orsubstantially parallel to the direction of circumferential extension ofthe tyre.

In a radially outer position with respect to the belt structure a treadband is applied, made from elastomeric material as well.

On the side surfaces of the carcass structure respective sidewalls ofelastomeric material are also applied, each one extending from one ofthe side edges of the tread band up to the respective annular anchoringstructure to the beads.

As is known, the tyres intended to be used on heavy load vehicles aretypically required to have optimal traction capability, acceleration,directionality and controllability characteristics, even on snowy or wetroad surfaces.

Another characteristic typically required to the tyres is a limited,and/or as much as possible uniform, wear, so as to increase theperformances of the tyres in terms of kilometric yield and reduce therunning and vibrations on travel.

The aforementioned characteristics in part contrast with each other. Inparticular, in practice it is not possible to ensure optimalperformances in terms of traction capability, acceleration,controllability and directionality without in some manner affecting thetyre performances in terms of kilometric yield and noise/vibrations.

The tyre performances on travel considerably depend on the design of thetread band thereof.

Typically, the tread band of a tyre comprises an annular central portionastride the equatorial surface of the tyre and two annular shoulderportions arranged on axially opposite sides with respect to theaforementioned annular central portion and separated from the latter byrespective circumferential groove.

The tread band moreover comprises a plurality of grooves and sipesarranged transversally and circumferentially in order to define a treaddesign. The aforementioned grooves and sipes define a plurality ofblocks in the tread design.

The circumferential and transversal sipes typically have a shape such todefine, in the adjacent blocks, respective mutual embedding orconstraining portions, both in circumferential direction and in axialdirection. The embedding in the circumferential direction contributes togive stability to the tyre, above all in the travel direction, while theembedding in the axial direction contributes to confer stability to thetyre particularly in the lateral direction. Such stability isessentially given by the lesser mobility of the blocks in theground-contacting area of the tyre due to the mutual abutment betweencontiguous blocks caused by the closure of the sipes.

Throughout the present description and in the subsequent claims, theterm: “block”, is used to indicate a tread band portion delimited byconsecutive grooves or sipes both in an axial and circumferentialdirection, the “groups of block” being instead circumferentiallydelimited by two subsequent transversal grooves and formed by a numberof blocks which are circumferentially aligned and separated bytransversal sipes.

Throughout the present description and in subsequent claims, the terms:“grooves” and “sipes”, are used to indicate channels formed in the treadband of the tyre, the transversal and circumferential sipes having awidth, respectively in a circumferential and transversal direction,lower than the width in a circumferential and transversal direction ofthe transversal and circumferential grooves.

Throughout the present description and in the subsequent claims,moreover, the terms: “axial” and “axially”, are used to indicate adirection substantially orthogonal to the equatorial plane of the tyre,i.e. a direction substantially parallel to the rotation axis of thetyre. The terms: “radial” and “radially”, are instead used to indicate adirection substantially orthogonal to the rotation axis of the tyre andlying on a plane passing through such rotation axis, while the terms:“circumferential” and “circumferentially”, are used to indicate adirection substantially parallel to the equatorial plane of the tyrealong the annular extension thereof.

Throughout the present description and in the subsequent claims, theexpression: “ground-contacting area of the tyre”, is used to indicatethe portion of the peripheral surface of the tread band in contact withthe road surface.

While the circumferential grooves affect the behaviour of the tyre interms of lateral stability and directionality, the transversal groovesaffect the behaviour of the tyre in terms of traction capability andacceleration. The circumferential and transversal grooves moreoveraffect the water removal in the ground-contacting area of the tyre whilerunning over wet road surfaces, reducing the aquaplaning phenomena.

A high contribution in terms of traction capability and acceleration isgiven to the tyre by the grip fronts defined on the tread band by thetransversal sipes. Such sipes also contribute, in case of wet roadsurface, to the water removal.

In the case of snowy road surface, the transversal sipes among otherthings ensure the trapping of the snow in the ground-contacting area ofthe tyre, so as to make on travel a contact between tyre and roadsurface of snow/snow type, such a type of contact being desired as itconfers greater traction capability to the tyre. In fact, during therolling of the tyre, the transversal sipes entering theground-contacting area of the tyre are closed due to the mobility of theblocks under the ground-contacting area of the tyre, in such a mannertrapping the snow, to then be opened by exiting the ground-contactingarea of the tyre.

Throughout the present description and subsequent claims, the terms:“entering” and “exiting”, are used to indicate—with reference to theground-contacting area of the tyre and with regard to the structuralcharacteristics of the blocks of the tread band (or of the transversalsipes)—those portions of the blocks which are first stressed or are thefirst entering in, contact with the road surface during the rolling ofthe tyre (or the transversal sipes adjacent to such block portions) and,respectively, the block portions which are last stressed or are the lastabandoning the contact with the road surface (or the transversal sipesadjacent to those block portions).

US 2007/0095447 discloses a tread band for tyres provided with groups ofblock delimited by circumferential and transversal grooves, such groupsof blocks being in turn provided with sipes with a variable profile in aradial and axial direction. In particular, the profile of these sipesvaries in an axial direction with a sinusoidal progression having aconstant pitch, while in radial direction it varies between a radiallyouter portion of the groups of blocks wherein the sipe has, in acircumferential direction, a predetermined width and a radially innerportion of the groups of blocks wherein the sipe has, always in acircumferential direction, a greater width.

EP 1 669 217 discloses a tread band for winter tyres, comprising aplurality of groups of blocks defined between a plurality ofcircumferential grooves and a plurality of transversal grooves. Eachgroup of blocks comprises a plurality of transversal sipes having aprofile with a substantially zigzag progression both in the axialdirection and radial direction.

US 2003/0201048 discloses a tread band for winter tyres, comprising aplurality of blocks defined between transversal grooves, each blockcomprising a sipe of lower width than that of the transversal groovesand depth substantially equal to that of the transversal grooves. Thesipe has a profile with a substantially zigzag progression both in theaxial direction and radial direction.

The Applicant observed that a high number of transversal sipes having ashape such as to define, in the adjacent blocks, mutual embeddingportions, if on one hand can be advantageous for the improvement of thetyre performances in terms of traction capability, acceleration, snowtrapping, water removal and lateral stability, on the other hand canlead to a decline of the tyre performances in terms of kilometric yield,as well as the rise of disturbing vibrations and noise due to theexcessive and/or irregular wear of the tread band.

The Applicant is convinced that such decline of the tyre performancesoccurs particularly due to the continuous mutual friction of the wallsof the adjacent blocks during opening and closing of the transversalsipes, respectively in the steps of exiting from, and entering in, theground-contacting area of the tyre. On the other hand, the Applicant isconvinced that, in order to enhance the performances of the tyre interms of lateral stability, traction capability and acceleration onsnowy or wet surfaces, and water removal on wet surfaces, it isadvantageous to make use of transversal sipes having a profile such asto permit an adequate mutual embedding of the adjacent blocks and asufficient opening and closing of the sipe at the ground-contacting areaof the tyre.

In order to satisfy the aforementioned partly contrasting needs, theApplicant has designed a tread design comprising appropriately shapedtransversal sipes in order to achieve the embedding between the adjacentblocks only at zones of the blocks where it has been found to beadvantageous to have the embedding, so as to obtain the desiredperformances of the tyre in terms of lateral stability, tractioncapability and acceleration on snowy or wet surfaces and water removalon wet surfaces. In such design, the profile of the transversal sipe issuch that the opening of the transversal sipes exiting from theground-contacting area of the tyre is in some manner controlled, so asto limit as much as possible the friction of the walls of the adjacentblocks and thus limit the wear of the tread band, in this mannerincreasing the kilometric yield of the tyre and reducing the possibilitythat undesired noise and vibrations rise.

In particular, the Applicant has found that it is possible to obtain atyre having optimal characteristics, either in terms of tractioncapability, acceleration, snow trapping, water removal and lateralstability, and in terms of kilometric yield and wear, using a treaddesign comprising transversal sipes having a profile such that theembedding between the adjacent blocks occurs in an accentuated manner atthe axially outer portions of the blocks and is progressively reducedmoving towards the centre of the sipe, and wherein the opening of thesipes occurs only up to a certain point, such an opening beingafterwards obstructed by the mutual contact of the walls of the adjacentblocks.

The present invention therefore relates, in a first aspect thereof, to atyre for vehicle wheels having a tread band comprising an annularcentral portion astride an equatorial plane and two annular shoulderportions arranged on axially opposite sides with respect to the annularcentral portion, the annular central portion being separated from eachannular shoulder portion by a respective circumferential groove, whereinthe annular central portion comprises a plurality of blocks, arrangedalong at least one circumferential row comprised between twocircumferential grooves, and at least one transversal sipe adapted todefine two circumferentially consecutive blocks, wherein the transversalsipe has a main surface oriented in a substantially radial direction andprovided with at least one deformation defining, in the adjacent blocks,respective portions of mutual constraint, wherein said deformation hasan overall decreasing width from an axial end of the sipe to a centralzone thereof and wherein said deformation has a radial extension lowerthan that of said main surface.

Throughout the present description and in the subsequent claims, theterm: “deformation”, is used to indicate, with reference to a mainsurface of the transversal sipe, a deviation from such main surface,along an inclined direction with respect to said surface, such as forexample a substantially circumferential direction, having a radialextension lower than that of the transversal sipe.

Throughout the present description and in the subsequent claims, withthe expression: “overall decreasing width from one axial end of the sipeto a central zone thereof”, it is meant that, considering any position Pbetween that end and that central zone, it is possible to identify aninterval I₀ of axial extension E around such position P such that theaverage width in a circumferential direction of the deformation in theinterval I₀ is greater than the average width in circumferentialdirection of the deformation in any interval I_(n) having the same axialextension E and placed closer to the central zone of the sipe withrespect to the interval I₀.

Such definition, therefore, covers the condition for which the width ofthe deformation is simply decreasing from the axial end of the sipe tothe central zone thereof, as well as the condition for which the widthof the deformation is variable in an oscillating manner from a minimumto a maximum in intervals I between the axial end and the central zoneand at least said maximums are decreasing from the axial end of the sipeto the central zone thereof.

Advantageously, the transversal sipe of the tyre of the presentinvention has a profile such that the mutual constraint between theadjacent blocks is progressively reducing from the axially outer zone ofthe sipe moving towards the centre of the sipe. The opening of the sipein the exiting step from the ground-contacting area is therefore greaterat the central zone thereof, and is progressively reducing towards theaxial end thereof. A sufficiently wide sack is therefore produced in thecentral zone of the sips so as to permit the trapping and maintaining ofthe snow—thus attaining the desired performances of the tyre in terms oftraction capability and acceleration on snowy road surfaces and waterremoval on wet road surfaces. Moreover, a mutual constraint between thecircumferentially consecutive blocks at the axially outer zone of thesipe is obtained which is sufficiently strong to stiffen the lateralfronts of the blocks of the tread band, thus attaining the desiredperformances of the tyre in terms of lateral stability.

In addition thereof, the particular profile of the transversal sipe ofthe tyre of the present invention allows, in the exiting step from thetyre ground-contacting area, preventing the opening of the sipes beyonda certain limit. This limit is reached when the walls of the mutualconstraining portions of the blocks adjacent to the sipe come intocontact with each other, mutually obstructing each other. A controlledopening of the sipes is therefore obtained, with a consequent reductionof the wear caused by the mutual friction of the walls of the adjacentblocks in the opening and closing step of the sipe. Thus, it followsthat an increase of the kilometric yield of the tyre and an attenuationof the problems related to undesired noise and vibrations is attained.

The tyre of the present invention is particularly adapted to be used indriving wheels of heavy load vehicles, but it can also be convenientlyused in the directional wheels of such vehicles.

In a second aspect thereof, the present invention relates to a treadband for a tyre for vehicle wheels comprising an annular central portionastride an equatorial plane and two annular shoulder portions arrangedon axially opposite sides with respect to the annular central portion,the annular central portion being separated from each annular shoulderportion by a respective circumferential groove, wherein the annularcentral portion comprises a plurality of grooves, arranged along atleast one circumferential row comprised between two circumferentialgrooves, and at least one transversal sipe adapted to define twocircumferentially consecutive blocks, wherein the transversal sipe has amain surface oriented in a substantially radial direction and providedwith at least one deformation defining, in the adjacent blocks,respective portions of mutual constraint, wherein said deformation hasan overall decreasing width from an outer end of the sipe to a centralzone thereof and wherein said deformation has a radial extension lowerthan that of said main surface.

Advantageously, such a tread band can be used as a premoulded tread bandfor covering worn tyres of heavy load vehicles wheels.

The present invention, in at least one of the aforementioned aspects,can have at least one of the following preferred characteristics.

In some embodiments of the present invention, the main surface of thetransversal sipe is substantially flat.

In preferred embodiments of the present invention, such main surfacecomprises a deviated portion at the central zone thereof.Advantageously, the deviated portion define a constraint between thecircumferentially consecutive blocks against the lateral stresses of thesame row, giving lateral stability to the tyre, and increases thesurface extension of the central zone of the sipe, allowing a greatersnow accumulation in such a zone of the sipe.

Preferably, a radially outer portion of the main surface of thetransversal sipe is not affected by the aforementioned deformation. Atthe outer surface of the tread band, therefore, no embedding occursbetween the circumferentially consecutive blocks; in this zone, themaximum opening of the sipe is thus achieved, this being advantageousfor the snow trapping.

Preferably, the central zone of the main surface of the transversal sipeis not affected by the aforementioned deformation. At the centre of thesipe, therefore, no embedding occurs between the circumferentiallyconsecutive blocks; in this zone, therefore, the maximum opening of thesipe is achieved, which can then trap the snow.

Preferably, the deformation of the main surface of the sipe extendsradially more outwardly, proceeding from the end of the sipe towards thecentral zone thereof. Advantageously, the surface extension of theembedding between the circumferentially consecutive blocks is in such amanner increased, axial extension of the sipe being equal, with evidentadvantages in terms of lateral stability of the tyre.

In the preferred embodiments of the present invention, the deformationof the main surface of the sipe comprises at least one bent portion witha progressively decreasing width from the end of the sipe to the centralzone thereof.

In some preferred embodiments, the deformation of the main surface ofthe sipe comprises a pair of bent portions placed side by side, whichare radially spaced apart from one other and extended on a same side ofthe main surface of the sipe. Advantageously, the provision of more bentportions allows improving the embedding between the blocks, withimportant advantages in terms of lateral stability of the tyre.

In other preferred embodiments, the deformation of the main surface ofthe sipe comprises a pair of bent sections placed side by side, whichare radially spaced apart from one other and extended on opposite sidesof the main surface of the sipe.

In further preferred embodiments, the deformation of the main surfacecomprises a pair of bent portions placed side by side, which areradially contiguous and extended on opposite sides of the main surfaceof the sipe.

In some particularly preferred embodiments, the deformation of the mainsurface comprises two pairs of bent portions placed side by side, eachpair comprising two bent portions which are radially contiguous andextended on opposite sides of the main surface of the sipe, the twopairs being radially spaced apart from one other.

Preferably, the two bent portions have different circumferential width.More preferably, the radially innermost bent portion has a width lowerthan that of the radially outer bent portion. In this manner, a greaterembedding is achieved at the radially outer portions of the sipe and alower embedding is achieved at the radially inner portions of the sipe.Such configuration is particularly advantageous considering the factthat, when the tyre is new, the radial extension and the mobility of theblocks is high and there is the maximum opening of the sipe. It is thusconvenient in these conditions to have the maximum embedding between thewalls of the circumferentially consecutive blocks. As the tread band isworn, the radial extension and mobility of the blocks is reduced; inthese conditions it is advantageous to have a lower embedding.

In some alternative embodiments of the present invention, thedeformation of the main surface of the transversal sipe comprises asuccession of embossed portions having a decreasing width from the endof the sipe towards the central zone thereof. The form of the embossedportions can be of various type, for example prismatic, pyramid,circular, conical etc.

In particularly preferred embodiments of the present invention, the mainsurface of the transversal sipe comprises at least two deformations,each one extended from one of the axial ends of the transversal sipe tothe central zone. Advantageously, the embedding of the circumferentiallyconsecutive blocks is in this case achieved at both axial ends of theblocks, further improving the tyre performances in terms of lateralstability.

Preferably, the deformations of the main surface of the transversal sipewhich extend from opposite ends are provided at radially offsetpositions, attaining in this manner a further advantageous stiffening ofthe tyre against the lateral stresses.

In all the preferred embodiments of the present invention, thedeformation of the main surface of the transversal sipe can beadvantageously defined by a curved surface. In this manner the presenceof corners is avoided, which can cause undesired tension concentrations,irregular wear problems and extractions problems of the sipe from themould.

Preferably, the tread band of the tyre of the present inventioncomprises, in the annular central portion thereof, at least twocircumferential rows of blocks, such rows being axially separated by acircumferential sipe. Advantageously, the circumferential sipe givesstability to the tyre in the travel direction.

Preferably, the tread band comprises a first circumferential grooveastride the equatorial surface of the tyre and two secondcircumferential grooves arranged on axially opposite sides with respectto the first circumferential groove, the circumferential rows of blocksbeing arranged between the first circumferential groove and each of thesecond circumferential grooves.

The particular design of the tread band described above can be appliedboth in winter tyres and in city tyres.

Preferably, in the case of winter tyres, the tread band comprises groupsof blocks separated by transversal grooves. Advantageously, such groovesdefine grip fronts which give to the tyre greater traction capabilityand acceleration on snowy or wet road surfaces, and allow an improvedsnow trapping and water removal.

Preferably, the aforementioned blocks have an elongated shape in theaxial direction.

Preferably, the groups of blocks of one circumferential row are atoffset circumferential positions with respect to the groups of blocks ofthe axially adjacent circumferential row, in order to give an improvedlateral stability to the tyre.

Preferably, each of the two annular shoulder portions comprises sipes ofidentical shape to, and different sizes of, the sipes of the annularcentral portion of the tread band.

On the other hand, in the case of city tyres, a transversal sipe isprovided between each block of a circumferential row and thecircumferentially consecutive block.

Preferably, the blocks have in this case an elongated shape in thecircumferential direction.

Preferably, the blocks of a circumferential row are at offsetcircumferential positions with respect to the blocks of the axiallyadjacent circumferential row, in order to give an improved lateralstability to the tyre.

Further characteristics and advantages of the present invention will beclearer from the following detailed description of some preferredembodiments of a tyre in accordance with the present invention, madewith reference to the attached drawings. In such drawings:

FIG. 1 shows a cross sectional view, made along the line I-I of FIG. 2,of a first embodiment of a tyre according to the invention;

FIG. 2 shows a plan development of a portion of the tread band of thetyre of FIG. 1;

FIG. 3 shows a plan development of a portion of the tread band of asecond embodiment of a tyre according to the invention;

FIG. 4 shows a perspective view of a first embodiment of a transversalsipe usable in the tread band of FIGS. 2 and 3;

FIG. 5 shows a side view of the sipe of FIG. 4;

FIG. 6 shows a perspective view of an alternative embodiment of atransversal sipe usable in the tread band of FIGS. 2 and 3;

FIG. 7 shows a perspective view of a further alternative embodiment of atransversal sipe usable in the tread band of FIGS. 2 and 3;

FIG. 8 shows a perspective view of a further alternative embodiment of atransversal sipe usable in the tread band of FIGS. 2 and 3;

FIG. 9 shows a side view of the sipe of FIG. 8;

FIG. 10 shows a side view of a further embodiment of a transversal sipeusable in the tread band of FIGS. 2 and 3.

In FIG. 1, a tyre for vehicle wheels according to the present invention,in particular a tyre intended to be used in the driving wheels of aheavy load vehicle, is on the whole indicated with 1.

Throughout the present description and in subsequent claims, theexpression “heavy load vehicle”, is used to indicate a vehicle belongingto the categories M2˜M3, N2˜N3 and O2˜O4 defined in “ConsolidatedResolution on the Construction of Vehicles (R.E.3) (1997)”, Annex 7,pages 52-59, “Classification and definition of power-driven vehicles andtrailers”, such as for example trucks, lorries, tractor trailers, buses,large vans and other vehicles of this type.

The tyre 1 comprises a carcass structure 2, including at least onecarcass ply 3 formed by reinforcing cords embedded in an elastomericmatrix.

The carcass ply 3 has opposite end edges 3 a engaged with respectivebead cores 4. The latter are situated in the zones 5 of the tyre 1normally identified with the name of “beads”.

On the outer perimeter edge of the bead cores 4, an elastomeric filling6 is applied which occupies the space defined between the carcass ply 3and the respective end edge 3 a of the carcass ply 3. The bead cores 4maintain the tyre 1 well fixed to the anchoring seat 7 which isspecifically provided in the wheel rim 8, thus preventing in operationthe bead 5 coming out from such seat 7.

Specific reinforcing structures (not illustrated) can be provided at thebeads 5, having the function of improving the torque transmission to thetyre 1.

A belt structure 9 is associated to the carcass ply 2 in a radiallyouter position thereof and preferably comprises a number of belt layers(in the specific illustrated example, two layers 9 i, 9 ii are shown)arranged radially one on top of the other and having textile or metalreinforcing cords with crossed orientation and/or substantially parallelto the direction of circumferential extension of the tyre.

A tread band 10 is applied to the belt structure 9 in a radially outerposition thereof, the tread band 10 being of elastomeric material aswell.

Moreover, respective sidewalls 11 of elastomeric material are applied onthe side surfaces of the carcass structure 2, each one extending fromone of the side edges 10 a of the tread band 10 up to the respectiveannular anchoring structure 4 to the beads 5.

With reference to the FIGS. 1-3, the tread band 10 comprises an annularcentral portion 10 i astride the equatorial plane Y-Y of the tyre 1 andtwo opposite annular shoulder portions 10 ii arranged in axiallyopposite sides with respect to the central annular portion 10 i.

The annular central portion 10 i of the tread band comprises acircumferential central groove 15 astride the equatorial plane Y-Y. Eachannular shoulder portion 10 ii is separated from the annular centralportion 10 i of the tyre 1 by a respective circumferential lateralgroove 16.

The tread band 10 comprises, at the annular central portion 10 ithereof, a plurality of blocks 20 arranged on opposite sides of thecircumferential central groove 15 and the circumferential lateralgrooves 16. In the following description, the blocks 20 will beindicated also with the expression: equatorial blocks.

With particular reference to FIGS. 2 and 3, the equatorial blocks 20 arearranged along circumferential rows 21 axially separated by respectivecircumferential sipes 22. In the specific example illustrated in FIGS. 2and 3, two rows 21 of blocks 20 are provided at each zone of the annularcentral portion 10 i comprised between the circumferential centralgroove 15 and each circumferential lateral groove 16.

Still at the annular central portion 10 i thereof, the tread band 10comprises a plurality of transversal sipes 30 interposed betweencircumferentially consecutive blocks 20.

The transversal sipes 30 extend along a direction substantiallyperpendicular to the equatorial plane Y-Y of the tyre 1. Throughout thepresent description and in the subsequent claims, with the expression:direction substantially perpendicular to the equatorial plane, it ismeant a direction which forms an angle with the equatorial planecomprised between 70° and 110°.

The tread design illustrated in FIG. 2 will now be described in moredetail. Such tread design is particularly adapted for being used in awinter tyre.

As illustrated in FIG. 2, the blocks 20 have a substantiallyparallelepiped shape, elongated in the axial direction.

The blocks 20 of each circumferential row 21 are grouped three by three,each group of blocks 20 comprising two transversal sipes 30 and beingcircumferentially separated from a consecutive group of blocks 20 of thesame row 21 by a respective transversal groove 23. For the sake ofclarity of illustration, the numeric reference 20 is associated onlywith some of the blocks, the numeric reference 30 is associated onlywith some of the transversal sipes and the numeric reference 23 isassociated only with some of the transversal grooves.

Preferably, as illustrated in FIG. 2, the groups of blocks 20 of acircumferential row are at offset circumferential positions with respectto the groups of blocks 20 of the axially adjacent circumferential row21. The circumferential grooves 16 and the circumferential sipes 22preferably extend over the entire circumferential extension of the tyre1 along a path forming a broken line defined by first circumferentialsections parallel to the equatorial plane Y-Y and second circumferentialsections inclines with respect to the equatorial plane Y-Y and joiningthe aforementioned first sections. In such a manner, the tractioncapability of the tread band 10 is advantageously increased in theforward direction of the tyre.

Preferably, some of the blocks 20 of the annular central portion 10 i ofthe tread band 10 of the example of FIG. 2 have a bevelled corner 24 atthe circumferential sipe 22. Other blocks 20 of the annular centralportion 10 i preferably have a bevelled corner 26 at the circumferentialgroove 16. Advantageously, the number of corners which could, due totheir mobility, trigger irregular wear and noise phenomena is thusappropriately reduced.

Preferably, the maximum depth of the tread band 10 (and thus, themaximum depth of the circumferential central groove 15, of thecircumferential lateral grooves 16, of the circumferential sipes 22 andof the transversal grooves 23) is comprised between about 10 mm andabout 25 mm, such depth being more preferably equal to about 22.5 mm.The depth of the transversal sipes 30 is preferably between 20% and 100%of the maximum depth of the tread band 10.

In particularly preferred embodiment of a tyre of the present inventionof the winter type, such as that illustrated in FIG. 2, the volumeoccupied by the blocks 20, or volume of the solids, in the annularcentral portion 10 i of the tread band, in a portion of the tread band10 having a length equal to the pitch of the tread design and a widthequal to the axial extension of the tread band, is comprised between 60%and 85% of the overall volume of such annular central portion 10 i(total volume). In the illustrated example, the ratio between the volumeof solids and the total volume is equal to about 68%.

Preferably, the aforementioned tyre further comprises, at each of thetwo annular shoulder portions 10 ii, a plurality of lateral blocks 25,also these being arranged along a respective circumferential row 27comprised between the circumferential groove 16 and a respective endportion 10 a of the tread band 10.

The lateral blocks 25 are grouped three by three, each block 25 of onegroup being separated from the circumferentially consecutive block ofthe same group by a lateral transversal sipe 35. Each group of blocks25, in turn, is separated from the circumferentially consecutive groupof blocks 25 by a lateral transversal groove 33.

The axial extension of the lateral blocks 25, of the lateral transversalsipes 35 and lateral transversal grooves 33 is greater than that,respectively, of the blocks 20, transversal sipes 30 and transversalgrooves 23 of the central annular portion 10 i of the tread band 10.

The groups of lateral blocks 25 are preferably offset in circumferentialdirection with respect to the groups of equatorial blocks 20 of the row21 arranged on the opposite side with respect to the circumferentialgroove 16.

Preferably, some of the lateral blocks 25 have a bevelled corner 36 atthe circumferential groove 16.

The tread design illustrated in FIG. 3 is now described in more detail.Such tread design is particularly adapted for being used in a city tyre.

The tread design of FIG. 3 differs from that of FIG. 2 only in thefeatures discussed below.

The blocks 20 preferably have a substantially parallelepiped shape,elongated in the circumferential direction and all of them are separatedfrom circumferentially consecutive blocks 20 by a respective transversalsipe 30. Comparing the tread design of FIG. 3 with that of FIG. 2, it isnoted how in the tread design of FIG. 3 circumferentially consecutivegroups of blocks comprised between transversal sipes corresponding tothe transversal sipes 23 of the tread design of FIG. 2 are notidentifiable.

The transversal sipes 30 have an inclination, with respect to theequatorial plane Y-Y of the tyre 1, preferably greater than that of thesipes of the tread design of FIG. 2. More preferably, the angle ofinclination of the transversal sipes 20 of the tread design of FIG. 3with respect to the equatorial plane Y-Y of the tyre is comprisedbetween 60° and 120°.

Preferably, the blocks 20 of a circumferential row 21 are at offsetcircumferential positions with respect to the blocks 20 of the axiallyadjacent circumferential row 21.

The central circumferential groove 15 preferably comprises a pluralityof ribs 40, extended from the bottom thereof, intended both to preventthe trigger of tearing in the rubber composition and to protect theunderlying belt structure. The circumferential sipes 22 preferablycomprise portions 35 of greater depth.

The circumferential grooves 16 and the circumferential sipes 22preferably extend over the entire circumferential extension of the tyre1 along a path forming a broken line having a substantially zigzagprogression, so as to give to an improved traction capability to thetyre in the forward direction.

Preferably, the maximum depth of the circumferential central groove 15and of the circumferential lateral grooves 16 is for example about 19.5mm, while that of the circumferential sipes 22 is preferably about 8 mm.The depth of the transversal sipes 30 is preferably lower than or equalto about 14 mm.

In the example shown in FIG. 3 of a tyre of the present invention of thecity type, the ratio between the volume of solids and the total volumeis equal to about 78%.

Preferably, the aforementioned tyre further comprises, at each of thetwo annular shoulder portions 10 ii thereof, a plurality of lateralblocks 55, also these being arranged along a respective circumferentialrow 56 comprised between the circumferential groove 16 and a respectiveend portion 10 a of the tread band 10.

The lateral blocks 55 are defined by lateral transversal sipes 60,preferably having a depth lower than or equal to about 7 mm.

Each block 55 in turn comprises a respective transversal sipe 65 havingan axial size lower than that of the lateral transversal sipes 60.

Preferably, the lateral transversal sipes 60 and the transversal sipes65 comprise respective ribs 61 and 66 extended from the bottom thereof.

The axial extension of the lateral sipes 65 and transversal sipes 60 isrespectively greater than that of the blocks 20 and of the transversalblocks 30 of the central annular portion 10 i of the tread band 10.

The lateral blocks 25 are preferably offset in circumferential directionwith respect to the equatorial blocks 20 of the row 21 arranged on theopposite side with respect to the circumferential groove 16.

Going back now to the tread design of FIG. 2, the transversal sipes 30of the annular central portion 10 i and the lateral transversal sipes 35of the annular shoulder portions 10 ii of the tread band 10 areidentical in shape. For an easier discussion and reading, throughout thepresent description the shape of such transversal sipes will bedescribed making explicit reference to the transversal sipes 30 of theannular central portion 10 i of the tread band 10, it being understoodthat what said is also applicable to the transversal sipes 35 of theannular should portion 10 ii of the tread band 10.

FIGS. 4 and 5 show a preferred embodiment of a mould portion adapted tomake in the tyre a transversal sipe 30 of the tread band 10 illustratedin FIG. 2.

In the following description, for an easier description, “ripe”indicates and represents both the sipe obtained on the tread design andthe portion of the mould adapted to obtain the sipe. In fact it shouldbe noted that the surfaces of the aforementioned mould portion areperfectly matched to the surfaces of the obtained sipe.

With particular reference to FIG. 4, the sipe 30 comprises a mainsurface 301 having a predetermined radial extension (or depth) H and apredetermined axial extension (or length) L. As already anticipated, thedepth H is preferably comprised between 20% and 100% of the maximumdepth of the tread band 10, while the length L is preferably equal tothat of the equatorial blocks 20.

The main surface 301 is preferably flat and has four deformations 302extended in a substantially perpendicular direction to a lying plane Pof the main surface 301. The deformations 302 are advantageously adaptedto define, in the two blocks 20 circumferentially adjacent to thetransversal block 30, respective portions of mutual embedding.

The number of deformations 302 of the main surface 301 can also bedifferent from four, a number of deformations between four and ten beinganyway preferred, in order to improve the embedding between the blocks20 which are circumferentially adjacent to the transversal spire 30.

The deformations 302 are defined by a first pair of bent portions 310and 311 placed side by side in the radial direction and by a second pairof bent portions 312 and 313 also placed side by side in the radialdirection and axially arranged on the opposite side to the bent portions310, 311 with respect to a centre plane M of the transversal sipe 30.

Preferably, the bent portions 310, 311, 312, 313 all have the same shapeand the same sizes.

The bent portions 310 and 311 extend on a same side of the main surface301 of the transversal sipe 30. Analogously, the bent portions 312 and313 extend on a same side of the main surface 301 of the transversalsipe 30, such side being the same on which the bent portions 310 and 311extend.

In an alternative embodiment of the transversal sipe 30, notillustrated, the bent portions 312 and 313 extend on a side of the mainsurface 301 opposite that on which the bent portions 310 and 311 extend.

In a further alternative embodiment of the transversal sipe 30, notillustrated, the bent portions 310 and 312 extend on a same side of themain surface 301, while the bent portions 311 and 313 extend on a sideof the main surface 301 opposite that on which the bent portions 310 and312 extend.

Preferably, the position of the bent portions 312 and 313 on the mainsurface 301 is offset, in the radial direction, with respect to that ofthe bent portions 310 and 311, so as to stiffen the tyre against thelateral stresses. Such characteristic is conveniently shown in FIG. 4,where it can be seen how at one axial end 30 a of the transversal sipe30, the radially inner end of the bent portion 310 is distant from theradially inner end of the transversal sipe 30 by a distance d4, while atthe opposite axial end 30 b of the transversal sipe 30, the radiallyinner end of the bent portion 312 is distant from the radially inner endof the transversal sipe 30 by a distance d8 which is greater than d4.Advantageously, the aforementioned offset contributes to the stiffeningof the tyre against the lateral stresses.

Each bent portion 310, 311, 312, 313 extends axially on the main surface301 of the transversal sipe 30 at a respective surface portion having anaxial extension d1, d3 preferably comprised between the 30% and 70% ofthe axial dimension L of the sipe. Therefore, the main surface 301 ofthe transversal sipe 30 has a central zone 303 which is not affected bythe deformations 302. Preferably, the aforementioned central zone 303has an axial dimension d2 comprised between about 1 mm and about 10 mm.

Moreover, preferably, the bent portions 310, 311, 312, 313 extend on themain surface 301 of the transversal sipe 30 so as not to affect aradially outer portion 304 of such main surface 301.

Advantageously, at the central zone 303 and radially outer portion 304of the main surface 301, the maximum opening of the transversal sipe 30is achieved, therefore attaining an optimal trapping of the snow at suchzones.

For an easier discussion and reading, due to the preferred shape andsize identity of the bent portions 310, 311, 312 and 313, throughout thepresent description preferred shape and size of such bent portions aredescribed in detail making specific reference to the bent portion 310and possibly to the bent portion 311, it being clear that what said isapplicable also to the other bent portions.

The bent portions 310 and 311 (and therefore also the bent portions 311and 312) have, at the axial end 30 a of the transversal sipe 30, aradial extension indicated in FIG. 4 with, respectively, d5, d7 andhaving a value preferably comprised between about 10 mm and about 80 mm.

The bent portions 310 and 311 are spaced apart by a main surface portion301 having a radial size d6 preferably greater than or equal to about 2mm.

The bent portion 310 is defined by a curved surface portion having awidth in a circumferential direction which progressively decreases,moving axially from the axial end 30 a of the transversal sipe 30towards a central zone 303 of the sipe 30, with a curvature radius R1preferably comprised between about 10 mm to about 80 mm.

Preferably, the width d11 at the axial end 30 a of the transversal sipe30 has a value comprised between about 1 mm and about 4 mm, such widthbeing progressively reduced in a circumferential direction moving fromthe axial end 30 a of the transversal sipe 30 towards its central zone303. In practice, the bent portion 310 has a shape substantially of anail.

Preferably, the bent portion 310 extends radially more towards theradially outer zone 304 of the main surface 301, proceeding from theaxial end 30 a of the transversal sipe 30 towards the central zone 303.Such characteristic is made evident in FIG. 4 by the fact that theradially inner end of the bent portion 310, at the boundary with thecentral zone 303 of the sipe 30 (such boundary being indicated in FIG. 4by the vertical dotted line) has a radial distance d9 from the radiallyinner end of the transversal sipe 30 greater than the sum of d4 and d5.Analogously, the radially inner end of the bent portion 311, at theboundary with the central zone 303 of the sipe 30, has a radial distanced10 from the radially inner end of the bent portion 310 greater than thesum of d6 and d7. Advantageously, the surface extension of the embeddingbetween the blocks 20 circumferentially adjacent to such sipe is thusincreased, axial extension of the transversal sipe 30 being equal, withimportant advantages in terms of lateral stability of the tyre.

With particular reference to FIG. 5, the bent portions 310 and 311 havein cross section a shape defined by three arcs of curved surfacesrespectively having curvature radii R2, R3 and R4, where R2 ispreferably equal to R4 and R3 preferably has a value comprised between0.3 and 3 mm.

FIG. 6 shows an alternative embodiment of the transversal sipe 30. Suchembodiment differs from that of FIGS. 4 and 5 only in that the mainsurface 301 has, at the central zone 303 thereof, a deviated portion320. Such deviated portion 320, in particular, is defined by a centralportion 301 c of main surface 301 inclined by a predetermined angle α1with respect to two opposite lateral portions 301 a and 301 b of mainsurface 301 lying on respective planes P1 and P2, which are parallel toeach other. The angle α1 is preferably comprised between 90° and 140°and the extension sb1 of the central portion 301 c of main surface 301(and therefore the width of the deviated portion 320) preferably has avalue comprised between about 1 mm and about 10 mm. In practice, due tothe deviated portion 320, the pairs of bent portions 310, 311 and 312,313 are placed at circumferentially offset positions.

Advantageously, the deviated portion 320 makes a constraint between thecircumferentially consecutive blocks against the lateral stresses,giving lateral stability to the tyre, and increases the surfaceextension of the central zone 303 of the sipe, allowing a greateraccumulation of snow in such zone of the sipe.

FIG. 7 shows a further alternative embodiment of the transversal sipe30. Such embodiment differs from that of FIG. 4 only in that the bentportions of each pair of bent portions 310, 311 and 312, 313 extend onopposite sides of the main surface 301 of the transversal sipe 30. Inparticular, in the specific example illustrated herein, the bentportions 310 and 313 extend on the same side of the main surface 301,while the bent portions 311 and 312 extend on the opposite side of themain surface 301.

FIGS. 8 and 9 show a further alternative embodiment of the transversalsipe 30. Such embodiment differs from that of FIG. 4 only in that eachbent portion 310, 311, 312 and 313 is defined by a pair of bent portionsplaced side by side, which are contiguous in a radial direction andextended on opposite sides of the main surface 301 of the sipe 30, suchpairs of bent portions being respectively indicated with 310′, 310″,311′, 311″, 312′, 312″, 313′, 313″.

As illustrated in FIG. 9, each pair of bent portions 310′, 310″ has anaxial section d5 equal to that of the bent portion 310 of the embodimentof FIG. 4, and is spaced apart from the radially adjacent pair of bentportions 311′, 311″ by portion of main surface 301 having a radialextension d6 equal to that of the portion which separates the bentportions 310 and 311 of the embodiment of FIG. 4. FIG. 9 also shows howeach pair of bent portion 311′, 311″ has an axial extension d7 equal tothat of the bent portion 311 of the embodiment of FIG. 4. Moreover, eachbent portion 310′, 310″ has a width d11 in the circumferential directionequal to that of the bent portion 310 of the embodiment of FIG. 4 and aradial extension d12 equal to about half the radial extension d5 of thebent portion 310 of the embodiment of FIG. 4.

FIG. 10 shows a further alternative embodiment of the transversal sipe30. Such embodiment differ from that of FIG. 4 only in that the radiallyinner bent portion 310 (and analogously the radially inner bent portion312, not visible in FIG. 10) has an extension d11 in the circumferentialdirection which is lower than the extension d13 of the radially outerbent portion 311 (and analogously of the radially outer bent portion313, not visible in FIG. 10), so as to make a greater embedding at theradially outermost portions of the transversal sipe 30 and a lowerembedding at the radially inner portions of the sipe 30. Suchconfiguration advantageously allows attaining, when the tyre is new andthus when the radial extension and mobility of the blocks is high, themaximum embedding between the walls of the circumferentially consecutiveblocks 20, such embedding being steadily reduced as the tread band,being worn, exhibits portions of stiffer blocks on the outer peripheralsurface thereof.

In an alternative embodiment of the present invention, not illustrated,the deformation of the main surface of the transversal sipe 30 comprisesa succession, in the axial direction, of embossing portions having acircumferential width which can vary in an oscillating manner from aminimum to a maximum between the axial end of the sipe and the centralzone thereof, each embossing portion in any case having a maximum widthprogressively decreasing from the axial end of the transversal sipe 30towards its central zone. The shape of the embossing portion can be ofvarious type, for example prismatic, pyramid, circular, conical etc.

What has been stated above with reference to the shape of thetransversal sipes 30 of the annular central portion 10 i of FIG. 2 isalso valid for the transversal sipes 30 of the central annular portion10 i of the tread band 10 of FIG. 3. However, unlike the annularshoulder portions 10 ii of the tread band of FIG. 2, which as statedabove have lateral transversal sipes 35 having a shape equal to that ofthe transversal sipes 30 of the annular central portion 10 i, thelateral transversal sipes 60 of the annular shoulder portions 10 ii ofthe tread band 10 of FIG. 3 have a shape which is different from that ofthe transversal sipes 30 of the annular central portion 10 i, such shapebeing in particular of conventional type.

The tread design illustrated in FIGS. 2 and 3 are only examples of ahigh number of tread designs which can be effectively made according tospecific requirements. In particular, the number of blocks, transversalsipes, circumferential sipes, transversal grooves (if present),circumferential grooves, rows of blocks and possible the number ofblocks of each group of blocks (if present), the circumferentialposition of the blocks of one row with respect to that of the blocks ofthe axially adjacent row and/or the circumferential position of theblocks of the annular central portion of the tyre with respect to thatof the blocks of the annular shoulder portions of the tyre can varyaccording to the intended specific use of the tyre, thus obtaining atread design which is different from that illustrated in FIGS. 2 and 3but which is always within the scope of protection defined by thefollowing claims. Tread designs can also be provided without the centralgroove 15, or with blocks, circumferential and transversal grooves (ifpresent) and circumferential sipes of a shape and/or size different fromthose described above with reference to FIGS. 2 and 3. Also theinclination of the transversal sipes with respect to the equatorialplane Y-Y can be different from that illustrated in FIGS. 2 and 3,always remaining within the scope of protection defined by the followingclaims.

Obviously, a man skilled in the art can make further modifications andvariants in order to satisfy specific and contingent requirements,variants and modifications which are still within the scope ofprotection as defined by the following claims.

1-27. (canceled)
 28. A tyre for a vehicle wheel, having a tread bandcomprising an annular central portion astride an equatorial plane andtwo annular shoulder portions arranged on axially opposite sides withrespect to the annular central portion, the annular central portionbeing separated from each annular shoulder portion by a respectivecircumferential groove, wherein the annular central portion comprises aplurality of blocks arranged along at least one circumferential rowbetween two circumferential grooves, and at least one transversal sipecapable of being adapted to define two circumferentially consecutiveblocks, wherein the transversal sipe has a main surface oriented in asubstantially radial direction and provided with at least onedeformation defining, in adjacent circumferentially consecutive blocks,respective portions of mutual constraint, wherein said deformation hasan overall decreasing width from an axial end of the sipe to a centralzone thereof, wherein said deformation has a radial extension smallerthan that of said main surface and extends radially more outwardlyproceeding from the axial end of the sipe toward the central zonethereof.
 29. The tyre according to claim 28, wherein the main surface isflat.
 30. The tyre according to claim 28, wherein the main surfacecomprises a deviated portion at the central zone thereof.
 31. The tyreaccording to claim 28, wherein a radially outer portion of the mainsurface of the transversal sipe is not affected by the deformation. 32.The tyre according to claim 28, wherein the central zone of the mainsurface of the transversal sipe is not affected by the deformation. 33.The tyre according to claim 28, wherein the deformation comprises atleast one bent portion having a progressively decreasing width from theend of the sipe to the central zone thereof.
 34. The tyre according toclaim 33, wherein the deformation comprises a pair of bent portionsplaced side by side, which are radially spaced apart from one other andextended on a same side of the main surface of the sipe.
 35. The tyreaccording to claim 33, wherein the deformation comprises a pair of bentportions placed side by side, which are radially spaced apart from oneother and extended on opposite sides of the main surface of the sipe.36. The tyre according to claim 33, wherein the deformation comprises apair of bent portions placed side by side, which are radially contiguousand extended on opposite sides of the main surface of the sipe.
 37. Thetyre according to claim 33, wherein the deformation comprises two pairsof bent portions placed side by side, each pair comprising two radiallycontiguous bent portions extended on opposite sides of the main surfaceof the sipe, the two pairs being radially spaced apart from one other.38. The tyre according to claim 34, wherein the bent portions of saidpair of bent portions placed side by side have a differentcircumferential width.
 39. The tyre according to claim 38, wherein aradially innermost bent portion has a width lower than that of aradially outermost bent portion.
 40. The tyre according to claim 28,wherein the deformation comprises a succession of embossed portionshaving a decreasing width from the end of the sipe to the central zonethereof.
 41. The tyre according to claim 28, wherein the main surface ofthe transversal sipe comprises at least two deformations, each oneextended from one of the axial ends of the transversal sipe to thecentral zone.
 42. The tyre according to claim 41, wherein thedeformations extended from opposite ends are provided at offset radialpositions.
 43. The tyre according to claim 28, wherein the deformationis defined by a curved surface.
 44. The tyre according to claim 28,comprising at least two circumferential rows of blocks in said annularcentral position, said at least two circumferential rows of blocks beingaxially separated by a circumferential sipe.
 45. The tyre according toclaim 44, comprising a first circumferential groove astride saidequatorial plane and two second circumferential grooves arranged onaxially opposite sides with respect to the first circumferential groove,said at least two circumferential rows of blocks being arranged betweenthe first circumferential groove and each of the second circumferentialgrooves.
 46. The tyre according to claim 28, wherein the blocks of saidat least one circumferential row are grouped together, each group beingseparated from a circumferentially consecutive group by a respectivetransversal groove.
 47. The tyre according to claim 46, wherein theblocks are elongated in an axial direction.
 48. The tyre according toclaim 46, comprising a first circumferential groove astride saidequatorial plane and two second circumferential grooves arranged onaxially opposite sides with respect to the first circumferential groove,said at least two circumferential rows of blocks being arranged betweenthe first circumferential groove and each of the second circumferentialgrooves, wherein the groups of blocks of a circumferential row are atoffset circumferential positions with respect to the groups of blocks ofan axially adjacent circumferential row.
 49. The tyre according to claim28, wherein each of two annular shoulder portions comprise sipes with ashape identical to, and a width different from, the sipes of the centralannular portion of the tread band.
 50. The tyre according to claim 28,comprising a transversal sipe between each block of said at least onecircumferential row and the circumferentially consecutive block.
 51. Thetyre according to claim 50, wherein the blocks are elongated in acircumferential direction.
 52. The tyre according to claim 50,comprising a first circumferential groove astride said equatorial planeand two second circumferential grooves arranged on axially oppositesides with respect to the first circumferential groove, said at leasttwo circumferential rows of blocks being arranged between the firstcircumferential groove and each of the second circumferential grooves,wherein the blocks of a circumferential row are at offsetcircumferential positions with respect to the blocks of an axiallyadjacent circumferential row.